I have previously proposed U.S. Pat. No. 5,307,541 relating to a so-called open type clamping device including a clamp band formed of metal strip material cut to a fixed length, the clamp band being wound in a circular ring for three-dimensionalization with its opposite ends overlapping each other, the bore diameter of the clamp band being artificially forcibly contracted by a draw operating type tool such as a pair of pliers, the opposite ends being then fixed together, thereby semipermanently fixing a part to be fixed, such as a fluid conveying hose for various fluids, dustproof bellows, shaft boot or the like, on the connecting circumferential surface of a mating part, such as a joint pipe, cock, or rotatable shaft.
In the case of this prior patent, whether in the basic embodiment or in modified embodiments, as is clear from the enlarged sectional views in FIGS. 9 and 28 of that patent, a prop key 23, 230 extends inwardly from the outer overlap portion 11b, 110b of a clamp band 11,110 while a receiving hole 14, 140 for the prop key 23, 230 is formed in the inner overlap portion 11a, 110a of the clamp band 11, 110, the arrangement being such that as soon as a disengaging force acts between a fixed tooth 22b, 220b and a seizing tooth 16a, 160a, the prop key 23, 230 quickly engages the opening edge of the receiving hole 14, 140, thereby preventing loosening or disengagement of the clamp band 11, 110.
However, as a result of repeated tests conducted under severe operating conditions to provide for commercial production, it has been found that since the prop key 23, 230 and the receiving hole 14, 140 therefor are interposed between a locked position where the fixed tooth 22b, 220b and seizing tooth 16a, 160a seizingly engage each other and a position where elastic humps 25 which are tension spring elements are bent up, overstretching or yielding of the elastic humps 25 under excessive load exceeding the elastic limit would lead to loosening, though not disengagement, of the clamp band 11,110; it is impossible for the prop key 23, 230 to prevent such loosening. That is, the prop key 23, 230 is practically nothing as it is incapable of preventing accidental loosening of the clamp band 11, 110. The reason is that the elastic humps 25 are bent up at a position closer to the location of the presence of the intermediate portion 11c, 110c of the clamp band 11, 110 where there is no overlap.
Further, in the aforesaid prior invention, one cut end of the inner overlap portion 11a, 110a of the clamp band 11, 110 is formed as a nose 12, 120 having a small fixed width W1, the nose 12, 120 being adapted to enter a nose receiving hole 21, 210 correspondingly formed in the outer overlap portion 11b, 110b during the bore diameter contracting operation on the clamp band 11, 110, with the result that there is no level difference produced in the surface of the clamp band 11, 110. However, since the nose 12, 120 is still in the form of a flat plate as a whole including its front end, it is still difficult for the nose to enter the nose receiving hole 21, 210 correctly and quickly, with the inner overlap portion 11a, 110a and outer overlap portion 11b, 110b of the clamp band 11, 110 tending to transversely deviate relative to each other.
Such positional deviation also makes it difficult for the fixed tooth 22b, 220b and seizing tooth 16a, 160a to seizingly engage each other correctly and quickly; therefore, there is a problem that the pilot function is inferior which is to lead the inner overlap portion 11a, 110a and outer overlap portion 11b, 110b of the clamp band 11, 110 to the correct overlap state.